NAPL
Detection

NAPL detection and thickness
measurement is often a critical environmental or engineering task. Non-aqueous phase liquid (NAPL) is
described as petroleum or other fluid that is immiscible in water and
tends to remain as a separate undissolved liquid in the
subsurface. The determination of the depth and
thickness of oil or other lighter than water fluid floating on groundwater
is wells or boreholes, especially monitoring wells, is accomplished by several
means. The method used is generally determined by accuracy
requirements and if a need for relatively rapid measurements
exists. Drillers often make an initial rapid measurement with
a "plopper" on the end of a length of twine. The
"plopper" consists of a cup shaped piece of metal that makes a
"plopping noise" when it hits the water. Knots in the
twine may indicate approximate depth intervals. The twine must
be lowered through the NAPL layer to measure the thickness. It is difficult
or impossible to determine the thickness of NAPL this way.
Another, somewhat more refined method involves coating the bottom of the
twine or a steel measuring tape with a compound that changes color when it is wet with NAPL that
contrasts with the part that is wet with water. This method can be
accurate, but it is slow and messy.

A clear bailer (transparent PVC or
Teflon) is sometimes used to sample and measure the thickness of NAPL.
This method is a good way to obtain a sample of the NAPL, but is not an an
accurate way to measure the thickness because of the disturbance that is
caused in the well.

Accurate measurements can
be collected more easily with an electronic "oil/water
interface" meter (or oil/water interface indicator or
probe). Interface meters generally detect the
oil/water interface by distinguishing the different angles of refraction of water and
NAPL. They generally signal if they are in NAPL or water with different
sound signals (eg. continuous beep versus short beeps) and/or light
signals (often both).

Our product
line includes Heron Instruments, Inc. products, manufacturers of oil/water interface
and water level meters. These instruments are required by many
of us in our daily work. With over thirty years of combined experience in the engineering,
hydrogeological, and equipment design fields, Heron Instruments has
developed the latest in water-level and oil/water interface meters.
Oil/water interface and water level meters by Heron demonstrate durability,
accuracy, and reliability. Heron Instruments may be ordered on this
site directly by credit
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Some small-diameter well solutions are explored on our "Small-Diameter
Well Quandray Page".